In recent years the television and radio broadcasting industries have begun to utilize communication satellites for broadcasting, as an alternative to standard broadcasting using broadcast satellites. Broadcast satellites and communication satellites are separated by a 50 to 60 degree radius in their respective stationary orbits over the equator. Communication satellites are attractive for use in broadcasting because there is typically only about a four degree difference in position between two such satellites. However, a drawback to using communication satellites is that their effective radiation power (dBW) is about 50 dBW in the center of Japan, which is about 10 dBW less than the standard radiation power of broadcast satellites (60 dBW). Thus, it is desirable to utilize an antenna that is capable of receiving waves from both communication and broadcast satellites.
An antenna for receiving electromagnetic waves simultaneously from a plurality of satellites located in different stationary orbit positions is shown in FIGS. 1A-1C. FIGS. 1A-1C depict front, top and side views of this type of antenna. As illustrated therein, an antenna 60 has a torus face 61 acting as a reflector, the torus face 61 having a plurality of focus points for the waves emanating from the satellites. Converters 2 and 3 each have a primary radiator located on the focus points corresponding to the direction of the waves coming from each satellite. Supporting arms 4 support the converters 2 and 3, while the antenna pole 5 supports the antenna 60 itself.
Antennas of the type employing a torus face or the like for a reflector are problematic in that they are expensive to manufacture and difficult to install. Particularly because of the complexity of the surface of a torus face, a tooling die for such a device is very costly.
Further, this type of prior art antenna is very difficult to properly install and adjust. Of course, it is well known that the direction of the antenna must be set so that a sufficient receiving sensitivity is obtained for the incoming satellite waves. This must be done upon initial installation of the antenna and during subsequent adjustments.
When an antenna is to receive waves from both communication and broadcast satellites, the antenna must be directed at the communication satellite. Moreover, this type of prior art antenna also requires that the converter for the broadcast satellite be set on a particular focus point of the antenna. Therefore, this type of antenna must also be directed to the broadcast satellite as well. In order to successfully accomplish this, an azimuth angle, an angle of elevation, and a polarization angle of the antenna direction must all be properly adjusted. This has proven to be sensitive, time consuming work.
Thus, there exists a need in the art for a multibeam antenna that not only can simultaneously receive electromagnetic waves from a plurality of satellites, of both the broadcast and communication type, but can also be manufactured at low cost and easily installed and adjusted.